/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 * <p>
 * http://www.apache.org/licenses/LICENSE-2.0
 * <p>
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.hadoop.hdfs.protocol;

import java.util.Arrays;
import java.util.List;

import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
import org.apache.hadoop.hdfs.StorageType;
import org.apache.hadoop.hdfs.security.token.block.BlockTokenIdentifier;
import org.apache.hadoop.hdfs.server.blockmanagement.DatanodeStorageInfo;
import org.apache.hadoop.security.token.Token;

import com.google.common.collect.Lists;

/**
 * Associates a block with the Datanodes that contain its replicas
 * and other block metadata (E.g. the file offset associated with this
 * block, whether it is corrupt, a location is cached in memory,
 * security token, etc).
 * <p>
 * 这个LocatedBlock就代表了一个block,他有多个副本,每个副本放在一个datanode上面
 * 同时这里也包含了block的其他的=元数据
 * 比如说:一个大文件拆成了多个block,这个block代表了这个大文件的哪一部分的内容,还有
 * 好比说这个block的数据是否破损了
 */
@InterfaceAudience.Private
@InterfaceStability.Evolving
public class LocatedBlock {

    private final ExtendedBlock b;
    // 代表在大文件中偏移量
    private long offset;  // offset of the first byte of the block in the file
    private final DatanodeInfo[] locs;
    /**
     * Storage ID for each replica
     */
    private final String[] storageIDs;
    // Storage type for each replica, if reported.
    private final StorageType[] storageTypes;
    // corrupt flag is true if all of the replicas of a block are corrupt.
    // else false. If block has few corrupt replicas, they are filtered and
    // their locations are not part of this object
    private boolean corrupt;
    private Token<BlockTokenIdentifier> blockToken = new Token<BlockTokenIdentifier>();
    /**
     * List of cached datanode locations
     */
    private DatanodeInfo[] cachedLocs;

    // Used when there are no locations
    private static final DatanodeInfo[] EMPTY_LOCS = new DatanodeInfo[0];

    public LocatedBlock(ExtendedBlock b, DatanodeInfo[] locs) {
        this(b, locs, -1, false); // startOffset is unknown
    }

    public LocatedBlock(ExtendedBlock b, DatanodeInfo[] locs, long startOffset,
                        boolean corrupt) {
        this(b, locs, null, null, startOffset, corrupt, EMPTY_LOCS);
    }

    public LocatedBlock(ExtendedBlock b, DatanodeStorageInfo[] storages) {
        this(b, storages, -1, false); // startOffset is unknown
    }

    public LocatedBlock(ExtendedBlock b, DatanodeInfo[] locs,
                        String[] storageIDs, StorageType[] storageTypes) {
        this(b, locs, storageIDs, storageTypes, -1, false, EMPTY_LOCS);
    }

    public LocatedBlock(ExtendedBlock b, DatanodeStorageInfo[] storages,
                        long startOffset, boolean corrupt) {
        this(b, DatanodeStorageInfo.toDatanodeInfos(storages),
                DatanodeStorageInfo.toStorageIDs(storages),
                DatanodeStorageInfo.toStorageTypes(storages),
                startOffset, corrupt, EMPTY_LOCS); // startOffset is unknown
    }

    public LocatedBlock(ExtendedBlock b, DatanodeInfo[] locs, String[] storageIDs,
                        StorageType[] storageTypes, long startOffset,
                        boolean corrupt, DatanodeInfo[] cachedLocs) {
        this.b = b;
        this.offset = startOffset;
        this.corrupt = corrupt;
        if (locs == null) {
            this.locs = EMPTY_LOCS;
        } else {
            this.locs = locs;
        }
        this.storageIDs = storageIDs;
        this.storageTypes = storageTypes;

        if (cachedLocs == null || cachedLocs.length == 0) {
            this.cachedLocs = EMPTY_LOCS;
        } else {
            this.cachedLocs = cachedLocs;
        }
    }

    public Token<BlockTokenIdentifier> getBlockToken() {
        return blockToken;
    }

    public void setBlockToken(Token<BlockTokenIdentifier> token) {
        this.blockToken = token;
    }

    public ExtendedBlock getBlock() {
        return b;
    }

    public DatanodeInfo[] getLocations() {
        return locs;
    }

    public StorageType[] getStorageTypes() {
        return storageTypes;
    }

    public String[] getStorageIDs() {
        return storageIDs;
    }

    public long getStartOffset() {
        return offset;
    }

    public long getBlockSize() {
        return b.getNumBytes();
    }

    void setStartOffset(long value) {
        this.offset = value;
    }

    void setCorrupt(boolean corrupt) {
        this.corrupt = corrupt;
    }

    public boolean isCorrupt() {
        return this.corrupt;
    }

    /**
     * Add a the location of a cached replica of the block.
     *
     * @param loc of datanode with the cached replica
     */
    public void addCachedLoc(DatanodeInfo loc) {
        List<DatanodeInfo> cachedList = Lists.newArrayList(cachedLocs);
        if (cachedList.contains(loc)) {
            return;
        }
        // Try to re-use a DatanodeInfo already in loc
        for (int i = 0; i < locs.length; i++) {
            if (locs[i].equals(loc)) {
                cachedList.add(locs[i]);
                cachedLocs = cachedList.toArray(cachedLocs);
                return;
            }
        }
        // Not present in loc, add it and go
        cachedList.add(loc);
        cachedLocs = cachedList.toArray(cachedLocs);
    }

    /**
     * @return Datanodes with a cached block replica
     */
    public DatanodeInfo[] getCachedLocations() {
        return cachedLocs;
    }

    @Override
    public String toString() {
        return getClass().getSimpleName() + "{" + b
                + "; getBlockSize()=" + getBlockSize()
                + "; corrupt=" + corrupt
                + "; offset=" + offset
                + "; locs=" + Arrays.asList(locs)
                + "; storageIDs=" +
                (storageIDs != null ? Arrays.asList(storageIDs) : null)
                + "; storageTypes=" +
                (storageTypes != null ? Arrays.asList(storageTypes) : null)
                + "}";
    }
}

